1. Field of the Invention
The present invention relates to an active matrix-driven type liquid crystal display panel.
2. Description of the Related Art
A liquid crystal display panel includes a liquid crystal interposed between a pair of substrates and forms an image by the application of voltages. The active matrix-driven type liquid crystal display panel includes a plurality of thin film transistors (TFT) as active elements. The thin film transistors are formed on one of the substrates together with gate bus lines, drain bus lines and pixel electrodes.
Each of the thin film transistors is provided with a gate electrode connected to the gate bus line, a gate insulation layer, a semiconductor active layer, a channel protective film, a drain electrode connected to the drain bus line and a source electrode connected to the pixel electrode. The channel protective film covers a central portion of the semiconductor active layer, and the drain electrode and the source electrode are connected to the semiconductor active layer on the outside of the channel protective film.
In a typical thin film transistor, an arm or projection extends perpendicular to the gate bus line to provide the gate electrode, while another arm or projection extends perpendicular to the drain bus line to provide the drain electrode. The source electrode is provided on the side of the semiconductor active layer opposite to the drain electrode and is connected to the pixel electrode. In this case, the gate electrode extends inwardly from the gate bus line so as to restrict the area in which the pixel electrode is to be formed, while the drain electrode extends inwardly from the drain bus line to restrict the area in which the pixel electrode is to be formed, thereby reducing an opening degree. Also, if the drain electrode, the source electrode and the joint region of the source electrode with the pixel electrode are aligned on line with each other, the area in which the pixel is to be formed is further restricted to further reduce the opening degree.
Alternatively, there is a case wherein the drain electrode of the thin film transistor is formed by the drain bus line itself. That is, the drain electrode is not formed by an arm or projection extending perpendicular from the drain bus line, but formed as part of a straight drain bus line. Accordingly, the area inside the drain bus line in which the pixel electrode is to be formed is widened to increase the opening size. In this case, if the source electrode is provided in parallel to the drain bus line, the size of the opening is increased.
Recently, there have been demands for liquid crystal display panels having high definition and high opening degree for displaying finer and brighter images, and therefore, the miniaturization of circuit patterns and the reduction in size of thin film transistors have proceeded. With a reduction in the size of the thin film transistors, the distance between an electrical contact point of the drain electrode with the semiconductor active layer and an electrical contact point of the semiconductor active layer with the source electrode is reduced, and static charge entering from the drain bus line may possibly discharge at the semiconductor active layer and break the TFT. Particularly, the drain electrode of the thin film transistor is formed by the drain bus line and, if the drain electrode crosses an end surface of the semiconductor active layer and the crossing point defines an electrical contact point between the drain electrode and the semiconductor active layer, so the distance between the electrical contact point of the drain electrode with the semiconductor active layer and the electrical contact point of the semiconductor active layer with the source electrode becomes extremely short, and therefore, breakage of the TFT is liable to occur.